I can’t find a specific image of it, only a reddit post talking about it, but in Grinch (2018) he buys green hair dye. I interpret that to mean he is just a normal whoville resident, but dyed green. I suppose his green grinch hair could be graying and he wants to look young, or he could just be some other color and chooses to be green, but I like to imagine him as some crazy naked hermit that makes himself green and everyone else just puts up with it.